Shares of Tetra Tech gained 6 percent Friday after an analyst upgraded the stock to “buy” from “neutral,” citing the Pasadena engineering firm’s growing project pipeline.

Debra Coy at Janney Montgomery Scott in Philadelphia said in a note to investors that the firm’s stock has slumped 21 percent since January when it lowered its financial projections for 2010. But she thinks the pessimism is unjustified given the company’s pipeline of contracts.

“We’ve learned that Tetra Tech has been selected to lead a team to design the replacement of Seattle’s downtown seawall, a $285 million project,” she wrote. “We believe the news flow will turn more positive in coming months.”

Coy has a 12-month target price of $26 on the Nasdaq stock, or 19 percent higher than its Friday close of $21.86.

The upgrade comes six weeks after analysts at Morgan Joseph upgraded Tetra Tech to “buy” with a target price of $25. Among the 18 analysts who cover the company eight give it a “buy” recommendation and 10 give it a “hold,”, according to Bloomberg News.